1. Field of the Invention
The present invention relates to a duty cycle detecting circuit for pulse width modulation (PWM), and more particularly to a detecting circuit that samples a PWM signal based on a clock frequency and calculates the duty cycle of the pulse width modulation signal based on the sampling results.
2. Description of the Related Art
Pulse Width Modulation (PWM) has been used extensively in electronic circuits including motor control circuits and power supply devices. In general, a pulse signal with a fixed frequency is used for controlling the ON and OFF states of a transistor. In a pulse width modulation system, a change of pulse width is used for determining the time interval of being active or cut-off for the transistor to achieve the control effect. In other words, the duty cycle of the PWM signal indicates a proportion of the active time (or high electric potential) of the pulse signal and plays an important role in the pulse width modulation system.
However, the duty cycle is very sensitive to many factors including an operating frequency, an operating temperature, a power voltage, and a circuit design. Therefore, it is an important subject to detect an actual duty cycle of a pulse signal in a pulse width modulation system under different operating conditions.